Texture Regulation of Metal-Organic Frameworks, Microwave Absorption Mechanism-Oriented Structural Optimization and Design Perspectives

Construction of 1D Molecular Conductive Wires Through a Polarized Gene Weaving Strategy for Efficient Electromagnetic Wave Absorption

The growing threat of electromagnetic pollution has become a pressing safety concern. Metal-organic framework (MOF) derivatives are considered ideal candidates for mitigating electromagnetic radiation. However, due to the limitations imposed by complex post-processing and disruption of pristine crystal structures, the mechanisms of electromagnetic wave absorption remain unclear, let alone achieving atomic-level regulation in MOF derivatives. Moreover, research on MOF-based electromagnetic wave absorbers (EMWA) has predominantly focused on 2D and 3D structures, leaving 1D MOFs largely unexplored. To address these challenges, a bottom-up polarization gene weaving strategy is proposed to integrate polarizable conjugated groups, thieno(3,2-b)thiophene (TBTT), into two types of conductive MOFs by fine-tuning self-assembly conditions. As expected, both MOFs exhibited strong natural polarization effects. Among them, the 1D linear coordination mode of CuTBTT-1D demonstrated enhanced charge carrier mobility and geometric effects compared to the 2D structure, CuTBTT-2D. The synthesized 1D molecular polarization wire, with a thickness of 2.2 mm, achieved ultra-high reflection loss (-77 dB) and super-wide absorption bandwidth (6.52 GHz). Its performance surpasses that of all known MOF-based EMWAs. This study provides a valuable strategy for the rational design of next-generation 1D MOF EMWA with atomic precision.

Regulation of PPy Growth States by Employing Porous Organic Polymers to Obtain Excellent Microwave Absorption Performance

Regulating the different growth states of polypyrrole (PPy) is a key strategy for obtaining PPy composites with high electromagnetic wave (EMW) absorption properties. This work finds that the growth states of PPy is regulated by controlling the amount of pyrrole added during the preparation of composites, so as to regulate the development of conductive networks to obtain excellent EMW absorption performance. The POP/PPy-200 composite achieves an effective absorption bandwidth (EAB) of 6.24 GHz (11.76-18.00 GHz) at a thickness of only 2.34 mm, covering 100% of the Ku band. The minimum reflection loss of -73.05 dB can be demonstrated at a thickness of only 2.29 mm, while at the same time showing an EAB of 5.96 GHz to meet the requirements of "thin", "light", "wide", and "strong". Such excellent EMW absorption performance is attributed to the conductive loss caused by the regulation of the growth states of PPy and the polarization loss caused by the heterostructure. This work also addresses the key challenge that porous organic polymers (POPs) cannot be applied to EMW absorption due to poor conductivity and providing new insights into the candidates for EMW absorbing materials.

Serial Nitrogen-Doped Metal/Carbon Composites Derived from Organic Salts for Superior Electromagnetic Wave Absorption and Supercapacitor Electrode

The present study provides a facile one-pot pyrolysis strategy to prepare serial nitrogen-doped (N-doped) metal/carbon composites derived from six types of metal ethylenediaminetetraacetic acid (EDTA-M, M = Co, Cu, Mn, Fe, Mg, and Ca). N-doped Co/C composite integrated carbonaceous with magnetic components to attain dielectric-magnetic double loss mechanisms. The minimum reflection loss and effective absorption bandwidth reached -57.6 dB at 1.75 mm and 4.64 GHz at 1.52 mm, respectively. The electromagnetic simulation further confirms that the dissipation ability increases with the improvement of carbonization temperature. Results show that altering the metal species of precursors can significantly improve the electrochemical performance of the composites using the identical strategy. N-doped Cu/C composite performed a maximum specific capacitance of 2383.3 F g-1 at 0.5 A g-1 -1, and maintained 86.3% cycling stability at 20 A g-1 after 5000 cycles. The energy density of a symmetrical two-electrode configuration achieved 350.13 Wh kg-1 at a power density of 4000.04 W kg-1. Density functional theory calculations indicate that nitrogen dopants cause faster ion transport and stronger adsorption capacity. Moreover, the bifunctionality of other composites types are also systematically characterized.

Highly hydrophilic and surface defect-rich MOF-74-PA15 obtained by phytic acid etching as a robust catalyst for the oxygen evolution reaction

Water splitting is an energy conversion process of vital importance. The oxygen evolution reaction (OER), as the half-reaction of water splitting, has very slow kinetics due to the complex quaternary electron transfer process involved, which greatly impedes the efficiency of energy conversion. The rational construction and modification of metal-organic frameworks (MOFs) offer a novel alternative for developing efficient OER electrocatalysts. In this study, MOF-74-PA15 with abundant surface defects and high hydrophilicity was successfully in situ constructed by etching MOFs for different reaction times using phytic acid (PA). The etching of PA increases the active area, and improves the hydrophilicity, allowing tighter contact between the material and the electrolyte. As a result, MOF-74-PA15 exhibits the most optimal OER catalytic performance in all the samples. The overpotential is 250 mV in 1 M KOH at 100 mA cm-2, with the lowest Tafel slope (35.59 mV dec-1). Furthermore, MOF-74-PA15 exhibits excellent stability. It maintains stability for 72 hours at a current density of 50 mA cm-2. This study presents a novel and feasible solution for modifying MOFs as electrocatalytic water splitting catalysts.

Fabrication of flower-like CoFe/C composites derived from ferrocene-based metal-organic frameworks: an in situ growth strategy toward high-efficiency electromagnetic wave absorption

Magnetic/dielectric composites can achieve high-efficiency electromagnetic wave (EMW) absorption performance by integrating multiple mechanisms such as dielectric loss and magnetic loss. The bimetallic metal-organic frameworks (MOFs) assembled from ferrocene (Fc) derivative-based bridging ligands are considered ideal precursors for the preparation of magnetic/dielectric composites due to tailored alloy components with magnetic losses. Herein, a novel CoFe/C composite with nanoflower structures is successfully obtained via an in situ growth strategy to decompose an Fc-based bimetallic MOF assembled from 1,1'-ferrocene dicarboxylic acid as bridging ligands and Co2+ ions. Notably, the nanoflower structures of the obtained composites provide an effective path for the scattering and reflection of the EMW, thereby improving the impedance matching by combining dielectric and magnetic loss. The CoFe/C composite exhibits excellent EMW absorption performance and has a minimum reflection loss of -61.6 dB at 3.7 mm and an effective absorption bandwidth of 6.24 GHz at a corresponding thickness of 2.2 mm. Moreover, the obtained composite exhibits lightweight characteristics and a low radar cross-section. This work presents a novel method through Fc-based bimetallic MOF derivatives to design and develop novel magnetic/dielectric composites with efficient EMW absorption properties for comprehensive applications.

Activating Excellent Electromagnetic Wave Absorption of Micromorphology-Optimized Cu/C Nanocomposite Fibers via a Metal-Organic Framework Template-Assisted Strategy

Morphological engineering is crucial for conceiving high-efficiency electromagnetic wave (EMW) absorption materials. However, for carbon fiber-based composites, the management of micromorphology is significantly astricted by complex fabrication. It remains highly challenging to clarify the micromorphological influences on the EMW loss mechanism of carbon fiber-based absorption materials. In this work, micromorphology-optimized Cu/C nanocomposite fibers are prepared by virtue of a metal-organic framework (MOF) template-assisted strategy. Through skillfully grafting the morphology-regulation capacity of MOFs onto composite fibers, the Oswald maturation and particle distribution issues of Cu nanoparticles are settled, and the efficient electron transport pathways are established by the bead-like structure of the fiber matrix. Compared to prepared conventional Cu/C nanocomposite fibers, the MOF template-assisted strategy stimulates a remarkable leap in EMW absorption performance. The minimum reflection loss value of Cu/C-40 can reach -64.5 dB, 15.96 times lower than that of a conventional sample (Cu/C-2). The maximum effective absorption bandwidth extends to 6.08 GHz, contrasting the ineffective performance of Cu/C-2. Systematic research demonstrates that the enabled graphite-catalytic function of Cu nanoparticles collaborated with an optimized conductive network structure plays a pivotal role in creating field-induced leakage currents, facilitating conductive loss, the primary contributor to EMW dissipation. This work establishes a correlation mechanism between micromorphology and EMW loss, presenting a compelling example of customizable carbon fiber-based absorbers.

Synchronous modification of ZIF-67 with cyclomatrix polyphosphazene coating for efficient flame retardancy and mechanical reinforcement of epoxy resin

Cyclomatrix polyphosphazenes have attracted widespread attention in the field of polymer flame retardancy. Nevertheless, the optimal manifestation of their distinctive structural attributes and flame-retardant properties necessitates a judicious selection of condensation monomers and synergistic templates during the fabrication of polyphosphazene flame retardants. In our previous studies, it was discovered that when ZIF-67 is functionalized with polyphosphazene, the by-product HCl from phosphazene polycondensation causes etching on ZIF-67. Based on this "synchronous etching" effect, a series of hybrid materials comprising cyclomatrix polyphosphazene and ZIF-67, denoted as ZIF-67@PDS (PDS, poly-(cyclotriphosphazene-co-4,4'-diaminodiphenyl sulfone)), ZIF-67@PBS (PBS, poly-(cyclotriphosphazene-co-Bisphenol A)), and ZIF-67@PZS (PZS, poly-(cyclotriphosphazene-co-4,4'-sulfonyldiphenol)), was synthesized utilizing DDS (4,4'-diaminodiphenyl sulfone), BPA (Bisphenol A), and BPS (4,4'-sulfonyldiphenol) monomers as precursors, respectively. Upon the incorporation of 2.0 wt.% of ZIF-67@PDS, ZIF-67@PBS, and ZIF-67@PZS, the flame retardant and mechanical characteristics of EP composites exhibited marked enhancement. The unique structural characteristics of hybrid and the synergistic effects of Co-P-N contribute to the improvement of comprehensive properties. Compared with pure EP, EP/ZIF-67@PZS has the best enhancement effect, and its pHRR, THR, and TSP decreased by 34.0%, 30.0%, and 40.5%, respectively. In terms of mechanical strength, ZIF-67@PZS also increases the flexural strength of EP by 37.42%. Relying on the "synchronous etching" effect, this study explores and verifies the effective combination of ZIF-67 and different types of polyphosphazenes, and obtains a series of ZIF-67-derived cyclomatrix polyphosphazene hybrids with different morphologies and properties in one step. It provides a new idea and strategy for the simultaneous modification of polyphosphazene materials and the preparation of multifunctional flame retardants in the future.

MOFs-Derived Strategy and Ternary Alloys Regulation in Flower-Like Magnetic-Carbon Microspheres with Broadband Electromagnetic Wave Absorption

Broadband electromagnetic (EM) wave absorption materials play an important role in military stealth and health protection. Herein, metal-organic frameworks (MOFs)-derived magnetic-carbon CoNiM@C (M = Cu, Zn, Fe, Mn) microspheres are fabricated, which exhibit flower-like nano-microstructure with tunable EM response capacity. Based on the MOFs-derived CoNi@C microsphere, the adjacent third element is introduced into magnetic CoNi alloy to enhance EM wave absorption performance. In term of broadband absorption, the order of efficient absorption bandwidth (EAB) value is Mn > Fe = Zn > Cu in the CoNiM@C microspheres. Therefore, MOFs-derived flower-like CoNiMn@C microspheres hold outstanding broadband absorption and the EAB can reach up to 5.8 GHz (covering 12.2-18 GHz at 2.0 mm thickness). Besides, off-axis electron holography and computational simulations are applied to elucidate the inherent dielectric dissipation and magnetic loss. Rich heterointerfaces in CoNiMn@C promote the aggregation of the negative/positive charges at the contacting region, forming interfacial polarization. The graphitized carbon layer catalyzed by the magnetic CoNiMn core offered the electron mobility path, boosting the conductive loss. Equally importantly, magnetic coupling is observed in the CoNiMn@C to strengthen the magnetic responding behaviors. This study provides a new guide to build broadband EM absorption by regulating the ternary magnetic alloy.

Artificial Intelligence-Guided Gut-Microenvironment-Triggered Imaging Sensor Reveals Potential Indicators of Parkinson's Disease

The gut-brain axis has recently emerged as a crucial link in the development and progression of Parkinson's disease (PD). Dysregulation of the gut microbiota has been implicated in the pathogenesis of this disease, sparking growing interest in the quest for non-invasive biomarkers derived from the gut for early PD diagnosis. Herein, an artificial intelligence-guided gut-microenvironment-triggered imaging sensor (Eu-MOF@Au-Aptmer) to achieve non-invasive, accurate screening for various stages of PD is presented. The sensor works by analyzing α-Syn in the gut using deep learning algorithms. By monitoring changes in α-Syn, the sensor can predict the onset of PD with high accuracy. This work has the potential to revolutionize the diagnosis and treatment of PD by allowing for early intervention and personalized treatment plans. Moreover, it exemplifies the promising prospects of integrating artificial intelligence (AI) and advanced sensors in the monitoring and prediction of a broad spectrum of diseases and health conditions.

Interfacial Engineering of Heterogeneous Reactions for MOF-on-MOF Heterostructures

Metal-organic frameworks (MOFs), as a subclass of porous crystalline materials with unique structures and multifunctional properties, play a pivotal role in various research domains. In recent years, significant attention has been directed toward composite materials based on MOFs, particularly MOF-on-MOF heterostructures. Compared to individual MOF materials, MOF-on-MOF structures harness the distinctive attributes of two or more different MOFs, enabling synergistic effects and allowing for the tailored design of diverse multilayered architectures to expand their application scope. However, the rational design and facile synthesis of MOF-on-MOF composite materials are in principle challenging due to the structural diversity and the intricate interfaces. Hence, this review primarily focuses on elucidating the factors that influence their interfacial growth, with a specific emphasis on the interfacial engineering of heterogeneous reactions, in which MOF-on-MOF hybrids can be conveniently obtained by using pre-fabricated MOF precursors. These factors are categorized as internal and external elements, encompassing inorganic metals, organic ligands, lattice matching, nucleation kinetics, thermodynamics, etc. Meanwhile, these intriguing MOF-on-MOF materials offer a wide range of advantages in various application fields, such as adsorption, separation, catalysis, and energy-related applications. Finally, this review highlights current complexities and challenges while providing a forward-looking perspective on future research directions.

Tailoring Built-In Electric Field in a Self-Assembled Zeolitic Imidazolate Framework/MXene Nanocomposites for Microwave Absorption

Heterointerface engineering, which plays a pivotal role in developing advanced microwave-absorbing materials, is employed to design zeolitic imidazolate framework (ZIF)-MXene nanocomposites. The ZIF-MXene composites are prepared by electrostatic self-assembly of negatively charged titanium carbide MXene flakes and positively charged Co-containing ZIF nanomaterials. This approach effectively creates abundant Mott-Schottky heterointerfaces exhibiting a robust built-in electric field (BIEF) effect, as evidenced by experimental and theoretical analyses, leading to a notable attenuation of electromagnetic energy. Systematic manipulation of the BIEF-exhibiting heterointerface, achieved through topological modulation of the ZIF, proficiently alters charge separation, facilitates electron migration, and ultimately enhances polarization relaxation loss, resulting in exceptional electromagnetic wave absorption performance (reflection loss RLmin = -47.35 dB and effective absorption bandwidth fE = 6.32 GHz). The present study demonstrates an innovative model system for elucidating the interfacial polarization mechanisms and pioneers a novel approach to developing functional materials with electromagnetic characteristics through spatial charge engineering.

Toward Enhancing Performance of Electromagnetic Wave Absorption for Conductive Metal-Organic Frameworks: Nanostructure Engineering or Crystal Morphology Controlling

Conductive metal-organic frameworks (cMOFs), which have high porosity and intrinsic electron conductivity, are regarded as ideal candidates for electromagnetic wave (EMW) absorption materials. Controlling the nanostructure of absorbers may be one of the effective strategies to improve the electromagnetic wave (EMW) absorption performance. Herein, a series of conductive Cu-HHTP MOFs (HHTP = 2,3,6,7,10,11-hexahydroxytriphenyl hydrates) with different nanostructures or crystal morphologies were successfully synthesized by using different structural inducers to regulate the changes in the morphology, thereby improving the EMW absorption performance. Specifically, when ammonia was used as an inducer, the obtained A-Cu-HHTP with a nanosheet structure exhibited excellent EMW absorption performance. The minimum reflection loss (RLmin) can reach -51.08 dB at 7.25 GHz with a thickness of 4.4 mm, and the maximum effective absorption bandwidth (EAB) can cover 5.73 GHz at 2.5 mm. The influence of the nanostructures of the cMOFs on the dielectric and EMW absorption performance was clarified. The nanosheet structure of A-Cu-HHTP increases its specific surface area, which expands multiple scattering and reflection paths of incident EMW; Meanwhile, the unique structure facilitates the formation of more heterogeneous interfaces, optimizing impedance matching. The significant improvement in EMW performance is mainly attributed to multiple reflections and scattering as well as impedance matching. This work not only provides a simple and effective strategy for improving electromagnetic wave absorption performance but also offers guidelines for preparing morphology functional cMOF materials.

Yolk-shell construction of Co0.7Fe0.3 modified with dual carbon for broadband microwave absorption

The rational and effective combination of multicomponent materials and the design of subtle microstructure for efficient microwave absorption are still challenging. In this study, carbon-coated CoFe with heterogeneous interfaces was space-restricted in the void space of hollow mesoporous carbon spheres through a facile approach involving electrostatic adsorption and annealing, and a high-performance microwave absorber (MAs) (denoted as Co0.7Fe0.3@C@void@C) was successfully prepared. The heterostructure, three-dimensional lightweight porous morphology, and electromagnetic synergy strategy enabled the Co0.7Fe0.3@C@void@C material with yolk-shell structure to exhibit surprising microwave absorption properties. When the annealing temperature and filler loading were 550° C and 15 wt%, respectively, the composites exhibited an effective absorption bandwidth (EAB) of 7.16 GHz at 2.48 mm and a minimum reflection loss of -24.1 dB at 2.11 mm. A maximum EAB of 7.21 GHz at 2.37 mm could be achieved for the composite prepared with an annealing temperature of 650° C. In addition, radar cross-section experiments demonstrated, the potential practical applicability of Co0.7Fe0.3@C@void@C. This work expands a new avenue to develop high-performance and lightweight MAs with ingenious microstructure.

The Developed Wave Cancellation Theory Contributing to Understand Wave Absorption Mechanism of ZIF Derivatives with Controllable Electromagnetic Parameters

How to better understand the influence of electromagnetic parameters on the absorbing properties of electromagnetic wave absorbers (EMAs) is an essential prerequisite for further synthesis and development of high-performance EMAs. In this work, an improved wave cancellation theory is used as a guiding principle to prepare N-doped carbon-coated cobalt nanoparticles (Co@NC) using ZIF-8@ZIF-67 as the precursor, thus enabling controllable electromagnetic parameters by regulating the conduction loss and dipole polarization ability. The Co@NC generated by pyrolysis at 700 °C under H2 atmosphere presents an optimized absorption performance. Benefiting from developed wave cancellation theory, the thickness of the film can be accurately adjusted so that the difference between the amplitude of the reflected and transmitted electromagnetic waves is only 0.001 and the phase difference is 180.05°, thus achieving a minimum reflection loss (RLmin (dB)) of -64.0 dB. Meanwhile, a maximum effective absorption bandwidth of 5.4 GHz is achieved simultaneously attributing to its most suitable electromagnetic parameters. Accordingly, the current research based on wave cancellation theory significantly contributes to understand the relationships between electromagnetic parameters and wave absorption properties, therefore providing a theoretical insight into the further development of high-performance EMAs.

Advancements in Microwave Absorption Motivated by Interdisciplinary Research

Microwave absorption materials (MAMs) are originally developed for military purposes, but have since evolved into versatile materials with promising applications in modern technologies, including household use. Despite significant progress in bench-side research over the past decade, MAMs remain limited in their scope and have yet to be widely adopted. This review explores the history of MAMs from first-generation coatings to second-generation functional absorbers, identifies bottlenecks hindering their maturation. It also presents potential solutions such as exploring broader spatial scales, advanced characterization, introducing liquid media, utilizing novel toolbox (machine learning, ML), and proximity of lab to end-user. Additionally, it meticulously presents compelling applications of MAMs in medicine, mechanics, energy, optics, and sensing, which go beyond absorption efficiency, along with their current development status and prospects. This interdisciplinary research direction differs from previous research which primarily focused on meeting traditional requirements (i.e., thin, lightweight, wide, and strong), and can be defined as the next generation of smart absorbers. Ultimately, the effective utilization of ubiquitous electromagnetic (EM) waves, aided by third-generation MAMs, should be better aligned with future expectations.

MOF-derived Co-C composites with 3D star structure for enhanced microwave absorption

The demand of microwave absorption materials (MAMs) with unique morphologies and electromagnetic (EM) balance has become necessary in recent years. Due to the ease of synthesis and tunable structure, metal-organic frameworks (MOFs) are widely used for this special MAMs. In this study, a new three-dimensional hybrid MOF is proposed that is co-doped with six equally branched star morphologies. The Co-C composite has the same six-branched morphology as that of the precursor. When the EM wave is incident, this special structure makes it easier for the EM wave to enter the material vertically due to the expansion of the incident surface, which is effective in adjusting the transmission path of the electron and the reflection and distribution of the EM wave. Because of the special morphology and magneto-dielectric synergy, the Co-C composite shows a minimum reflection loss (RLmin) of -48.5 dB at 11.0 GHz at an absorption thickness of 3.0 mm, with a microwave absorption bandwidth (EAB) of 6.1 GHz. This research provides a practical guidance for preparing the MAMs of special star structure.

Multifunctional MXene/C Aerogels for Enhanced Microwave Absorption and Thermal Insulation

Two-dimensional transition metal carbides and nitrides (MXene) have emerged as promising candidates for microwave absorption (MA) materials. However, they also have some drawbacks, such as poor impedance matching, high self-stacking tendency, and high density. To tackle these challenges, MXene nanosheets were incorporated into polyacrylonitrile (PAN) nanofibers and subsequently assembled into a three-dimensional (3D) network structure through PAN carbonization, yielding MXene/C aerogels. The 3D network effectively extends the path of microcurrent transmission, leading to enhanced conductive loss of electromagnetic (EM) waves. Moreover, the aerogel's rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXene-based absorbers. EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss (RLmin) value of - 53.02 dB (f = 4.44 GHz, t = 3.8 mm), and an effective absorption bandwidth (EAB) of 5.3 GHz (t = 2.4 mm, 7.44-12.72 GHz). Radar cross-sectional (RCS) simulations were employed to assess the radar stealth effect of the aerogels, revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m2. In addition to the MA performance, the MXene/C aerogel also demonstrates good thermal insulation performance, and a 5-mm-thick aerogel can generate a temperature gradient of over 30 °C at 82 °C. This study provides a feasible design approach for creating lightweight, efficient, and multifunctional MXene-based MA materials.

A review on composite strategy of MOF derivatives for improving electromagnetic wave absorption

To address the electromagnetic wave (EMW) pollution issues caused by the development of electronics and wireless communication technology, it is urgent to develop efficient EMW-absorbing materials. With controllable composition, diverse structure, high porosity, and large specific surface area, metal-organic framework (MOF) derivatives have sparked the infinite passion and creativity of researchers in the electromagnetic field. Against the challenges of poor inherent impedance matching and insufficient attenuation capability of pure MOF derivative, designing and developing MOF derivative-based composites by compounding MOF with other materials, such as graphene, CNTs, MXene, and so on, has been an effective strategy for constructing high-efficiency EMW absorbing materials. This review systematically expounds the research progress of MOF derivative-based composite strategies, and discusses the challenges and opportunities faced by MOF derivatives in the field of EMW absorption. This work can provide some good ideas for researchers to design and prepare high-efficiency MOF-based EMW absorbing materials in applications of next-generation electronics and aerospace.

Microwave absorbing characteristics of porphyrin derivates: a loop of conjugated structure

Microwave absorbing architectures have gained a great deal of attention due to their widespread application in diverse fields, especially in refining electromagnetic pollution. The aim of this study is to investigate the metamaterial characteristics of porphyrin derivatives as conjugated rings in the microwave region and evaluate the influence of electron-withdrawing and donating groups on microwave attenuating performance. Initially, an innovative microwave curing procedure was applied to synthesize the derivates; following that, the phenyl, aniline, and nitrophenyl-coupled structures were identified by XRD, FTIR, FESEM, and DRS analyses. The optical features illustrated that the characteristic band gap of the conjugated loops is obtained and that the optical performance can be manipulated by coupling the functional groups. Eventually, the achieved results demonstrated that the best microwave absorbing performance is related to aniline-coupled porphyrin with a maximum reflection loss (RL) value of -104.93 dB at 10.09 GHz with 2.80 mm in thickness attaining an efficient bandwidth (EB) (RL ≤ 10 dB) higher than the X-band. Noticeably, polyethylene (PE) was applied as an absorbing matrix presenting a meaningful idea for the development of practical microwave absorbers as a new generation of electromagnetic refining and stealth materials. The presented research provides precious inspiration to tailor novel microwave absorbing materials with metamaterial capability to promote their microwave absorbing performance.

In-situ magnetite deposited wood composites with extensive electromagnetic interference shielding performance

Wood is an insulator material, using its porous structure to endow it with efficient microwave absorption and broaden its application range is still a major challenge. Here, wood-based Fe₃O₄ composites with excellent microwave absorption properties and high mechanical strength were prepared by alkaline sulfite method, in-situ co-precipitation method and compression densification method. The results showed that the magnetic Fe₃O₄ was densely deposited in the wood cells, and the prepared wood-based microwave absorption composites had both high electrical conductivity, magnetic loss, excellent impedance matching performance and attenuation performance, as well as effective microwave absorption properties. In the frequency range of 2-18 GHz, the minimum reflection loss value was -25.32 dB. At the same time, it had high mechanical properties. Compared with the untreated wood, its modulus of elasticity (MOE) in bending increased by 98.77%, and modulus of rapture (MOR) in bending improved by 67.9%. The developed wood-based microwave absorption composite is expected to be used in electromagnetic shielding fields such as anti-radiation and anti-interference.

Ultrafine Vacancy-Rich Nb2O5 Semiconductors Confined in Carbon Nanosheets Boost Dielectric Polarization for High-Attenuation Microwave Absorption

The integration of nano-semiconductors into electromagnetic wave absorption materials is a highly desirable strategy for intensifying dielectric polarization loss; achieving high-attenuation microwave absorption and realizing in-depth comprehension of dielectric loss mechanisms remain challenges. Herein, ultrafine oxygen vacancy-rich Nb2O5 semiconductors are confined in carbon nanosheets (ov-Nb2O5/CNS) to boost dielectric polarization and achieve high attenuation. The polarization relaxation, electromagnetic response, and impedance matching of the ov-Nb2O5/CNS are significantly facilitated by the Nb2O5 semiconductors with rich oxygen vacancies, which consequently realizes an extremely high attenuation performance of - 80.8 dB (> 99.999999% wave absorption) at 2.76 mm. As a dielectric polarization center, abundant Nb2O5-carbon heterointerfaces can intensify interfacial polarization loss to strengthen dielectric polarization, and the presence of oxygen vacancies endows Nb2O5 semiconductors with abundant charge separation sites to reinforce electric dipole polarization. Moreover, the three-dimensional reconstruction of the absorber using microcomputer tomography technology provides insight into the intensification of the unique lamellar morphology regarding multiple reflection and scattering dissipation characteristics. Additionally, ov-Nb2O5/CNS demonstrates excellent application potential by curing into a microwave-absorbing, machinable, and heat-dissipating plate. This work provides insight into the dielectric polarization loss mechanisms of nano-semiconductor/carbon composites and inspires the design of high-performance microwave absorption materials.

Regulating conduction and polarization losses by adjusting bonded N in N-doped Cu/CuO/C composites

Conduction and polarization losses are the main forms of dielectric loss, and regulating these mechanisms is key to obtaining favorable electromagnetic wave absorption performance. In this study, the conversion of graphite N and pyridine N in Cu-based metal-organic framework (MOF)-derived composites was adopted to modulate conduction and polarization losses by tuning the pyrolysis temperature and Cu salt concentration. The results show that increasing the pyrolysis temperature facilitates the conversion of pyridine N to graphite N, which is beneficial for conduction loss. Moreover, increasing the Cu concentration promotes the transformation of pyridine N to graphite N as well as, and then promotes the reverse conversion of graphite N to pyridine N, which is conducive to defect-induced polarization. The unique layered Cu/CuO/C composite obtained at 700 °C with a moderate Cu content exhibited the optimal performance with an effective absorption bandwidth of 5.5 GHz (11.6 ∼ 17.1 GHz) at an ultra-thin thickness of 1.56 mm. This is owed to its favorable impedance matching, significant conduction loss, and polarization loss (defect-induced polarization and interfacial polarization). This study provides a novel strategy for regulating conduction and polarization losses.

Enhanced electromagnetic wave absorption of Fe3O4@MnO2@Ni-Co/C composites derived from Prussian blue analogues

Herein, Fe₃O₄@MnO₂@Ni-Co/C composites derived from PBAs were successfully fabricated. Firstly, Ni-Co Prussian blue analogues (Ni-Co PBAs) were used as precursors to derive a carbon layer on their surface by annealing treatment and subsequently translated into MnO₂@Ni-Co/C nanocubes after hydrothermal reactions. Fe₃O₄@MnO₂@Ni-Co/C composites were finally obtained after depositing Fe₃O₄ nanoparticles through the annealing process. Their electromagnetic wave (EMW) absorption performance apparently enhanced, thanks to the excellent impedance matching and strong attenuation derived from the synergy between the dielectric loss and the magnetic loss. In particular, the minimum reflection loss (RL_min) of Fe₃O₄@MnO₂@Ni-Co/C reached -41.2 dB with a thickness of 4.0 mm and the effective absorption bandwidth (EAB) reached 7.1 GHz with a thickness of 2.0 mm. Therefore, the results could be significant for synthesizing EMW absorbers with excellent performance, a broad bandwidth, strong absorption, thin thickness and light weight.

Fabrication of an Ultralight Ni-MOF-rGO Aerogel with Both Dielectric and Magnetic Performances for Enhanced Microwave Absorption: Microspheres with Hollow Structure Grow onto the GO Nanosheets

An ultralight Ni-MOF-rGO aerogel which possess the merits of not only broad bandwidth and strong absorption but also lightweight and thin matching thickness is fabricated through a hydrothermal treatment, freeze-drying, and annealing procedure. The Ni@C microspheres are dispersed randomly and evenly on the graphene oxide (GO) nanosheets, which can be proved through SEM and TEM results. The electromagnetic parameters of the composite can be adjusted by changing the mass ratio of the MOF and GO to endow the material with both good impedance matching and superior electromagnetic wave absorption performances. Consequently, the resulting composite shows outstanding microwave absorption performance, which achieves strong absorption (-51.19 dB) and broad effective absorption bandwidth (6.32 GHz) with a thickness of 1.9 mm while the filling content is only 2 wt %. In addition, the multiple loss mechanisms of the Ni-MOF-rGO aerogel are illustrated, including conduction loss, dipolar polarization, interfacial polarization, magnetic resonance, and eddy current loss. In a word, the extraordinary microwave absorption performance is ascribed to the synergistic effects of the unique multiple layered structure of GO and the hollow core-shell structure of the Ni@C microsphere. This work demonstrates that the ultralight aerogel with excellent electromagnetic wave absorption performance is a promising strategy for microwave absorption application.